Magnetically actuated devices, such as solenoid valves are used in many types of systems including automotive applications such as fuel injection, anti-lock braking and active suspension systems.
Magnetically actuated devices typically include a magnetic coil and a moving magnetic core or plunger. In a typical arrangement of a solenoid valve 10, as shown in FIG. 1, the coil 22 surrounds the plunger 28 such that when the coil 22 is energized with electric current, a magnetic field is induced in the interior of the coil 22. The plunger 28 is formed of a soft magnetic material, typically a ferritic steel. A spring (not shown) holds the plunger 28 in a first position such that the device is either normally open or closed. When the coil 22 is energized, the induced magnetic field causes the plunger 28 to move to a second position to either close the device, if it is normally open, or open it, if it is normally closed.
It is desirable that the material used to make the magnetic core have good soft magnetic properties, principally, a low coercive field strength to minimize “sticking” of the component and a high saturation induction to minimize the size and weight of the component.
The plunger is often in direct contact with the local environment such as the fluid that is being controlled. Many environments and fluids are corrosive and will corrode the plunger, which may cause the device to malfunction or the valve to leak or become inoperative. It is, therefore, desirable that the plunger be formed of a material that has good resistance to the corrosive influence of the environment in which it is to be used.
The increasingly frequent use of magnetically actuated valves in automotive technologies as fuel injection systems has created a need for a magnetic material having improved corrosion resistance. The need for better corrosion resistance is of particular importance in automotive fuel injection systems in view of the introduction of more corrosive fuels such as those containing ethanol or methanol.
It is known to use ferritic steels for the magnetic component of fuel injection valves, but the corrosion resistance has been found to be insufficient in corrosive fuel environments.